There has been known an information processing system that comprises an information processing unit that relays communications between a user terminal and another user terminal that the user terminal is desired to be connected, which are connected via an Internet Protocol (IP) network. For example, the information processing system of PTL 1 is described as comprising a Session Initiation Protocol (SIP) server as the information processing unit. Further, there has been known a technique that comprises a server for implementing Unified Communications (UC) as the information processing unit.